Superhard materials such as diamond are used in a wide variety of forms to machine, bore and degrade hard or abrasive work-piece materials. These materials may be provided as single crystals or polycrystalline structures comprising a directly sintered mass of grains of diamond forming a skeletal structure, which may define a network of interstices between the diamond grains. The interstices may contain a filler material, which may comprise a sintering aid for the diamond and possibly also a hard phase such as an inter-metallic or ceramic material. The filler material may be fully or partially removed in order to alter certain properties of the diamond structure material.
Various methods are known in the art for coating grains, particularly diamond grains with ceramic or metallic phases. For example, chemical vapour deposition (CVD), physical vapour deposition (PVD), sputter coating, fluidised bed methods and various methods involving the suspension of the grains in a liquid are well known. The last-mentioned approach includes electrolytic deposition, chemical electroless deposition, molten salt methods, and sol gel methods, which are taught in PCT publication numbers WO 2007/088461 and WO 2006/032982. CVD and PVD methods for coating abrasive grains, particularly diamond, are taught, for example in PCT publication numbers WO 2005/017227 and WO 2005/078045.
PCT publication number WO 2006/032982 discloses a method for coating abrasive grains, particularly cBN and diamond grains, with oxide, carbide, nitride, oxy-nitride, oxy-carbide or carbo-nitride material, as well as metals such as molybdenum and tungsten in elemental form.
There is a need for an efficient method for providing bodies comprising diamond having enhanced resistance to thermal degradation, and for such bodies, particularly but not exclusively for use as raw material for the manufacture of polycrystalline diamond material or a tool.